MOTN format comes from Apple Motion, which is integral part of Apple Final Cut Pro video editor and it is also only this software that can ne used for export of these files to standard multimedia formats, for example MP4. These files are essentially projects and thus tied to the original software only, which means there is no alternative.
if you struggle with working with .motn files or their export, it might be best to reach out to Apple support or Final Cut online community for further assistance.
Updated: October 24, 2023